A plasma process is a technique essential for manufacture of semiconductor devices. With recent demands for high integration and high speed of LSI, a design rule of semiconductor devices has been finer and finer and the size of semiconductor wafers has been increased. Accordingly, there is a need for a plasma processing apparatus to cope with such fineness and increase in size.
However, parallel-plate type or inductively-coupled plasma processing apparatuses have a difficulty in processing large diameter semiconductor wafers with plasma with uniformity and at a high speed.
For the purpose of avoiding such a difficulty, attention has been paid to a microwave plasma source which is capable of uniformly forming a surface wave plasma with high density and at a low electron temperature.
There has been proposed a microwave plasma processing apparatus which introduces a microwave from a microwave oscillator into a dielectric line via a waveguide and generates a plasma by supplying an electric field formed by the microwave below the dielectric line into a process chamber via an air gap and a microwave introduction window.
However, this microwave plasma processing apparatus requires a large space although it may process a large-scaled substrate. To solve this problem, there has been proposed a plasma processing apparatus which forms slots in a circumferential direction of an annular waveguide antenna and generates a plasma by introducing a microwave electric field into a process chamber via the slots and a microwave introduction window formed below the slots.
On the other hand, there has been proposed a plasma source in which a microwave is distributed, a plurality of microwave introduction mechanisms including respective tuners for impedance-matching in which the above-mentioned planar antennas are installed, and microwaves radiated therefrom are guided into the chamber and spatially composed inside the chamber.
Such spatial composition of the microwaves using the plurality of microwave introduction mechanisms individually adjusts the phase and intensity of the microwaves introduced from the microwave introduction mechanisms, thereby adjusting a plasma distribution with relative ease.
In addition, there has been proposed a technique in which a plurality of microwave introduction mechanisms is arranged to achieve a uniform plasma distribution.
However, the technique for introducing the microwave electric field into the process chamber via the slots arranged in the circumferential direction has a possibility that a plurality of surface wave modes appear, thus causing a mode jumping, which may result in an unstable plasma process.
Furthermore, in such techniques, a dielectric microwave transmission window (microwave transmission member) for each microwave introduction mechanism is installed in a ceiling wall of the chamber, and a microwave is radiated into the chamber via the microwave transmission window. However, this fails to sufficiently spread plasma in the circumferential direction, making it difficult to obtain a uniform plasma. It is also difficult to provide a single surface wave mode.